Oil and gas well drilling and servicing equipment, in the past, has made successful use of elongated cylindrically shaped battery packs which may be used with well tools to provide the power necessary for the operation of the downhole equipment.
Prior art battery packs may contain a plurality of cylindrically shaped energy cells which are physically arranged in an end to end relationship and are individually wired to suit the energy requirements of the equipment with which the battery pack is being used. Usually, the energy cells are connected by insulated conductive straps which are connected to each cell by welding or soldering and the individual cells are connected to a pair of bus conductors extending down the side of the battery pack. These connecting straps are usually insulated from the string of energy cells except where connections are being made. The energy cells and the strap connections are usually encased in some kind of tubular enclosure, such as paper or similar substance, in which the internal diameter of the enclosure is slightly greater than the diameter of the string of connected energy cells and the thickness of the bus connecting straps which pass along the side of the energy cells. The tubular enclosure is provided with a coating of an impervious material such as plastic and a sealed terminal structure is formed at one or both ends of the tubular enclosure.
Failure of prior art battery packs in the hostile environment in which they are forced to operate is usually due to fracture and leakage of the tubular enclosure securing the individual cells together. At times, the vibration in the medium surrounding the battery pack may cause the abrasion and fracture of the flat strap type bus conductors which connect the individual cells together, leading to open circuiting of the bus conductors and in some instances, short circuiting of the bus conductors and the resultant premature discharge of the battery pack. At times the failure of the bus conductors can produce an arc which may cause the battery pack to explode.
Although every attempt is made to seal the prior art battery packs against leakage of the surrounding medium into the interior thereof, when severe operating conditions are encountered, some of the corrosive components (i.e. hydrogen sulfide) of the surrounding medium may penetrate into the interior of the battery pack causing components of the battery pack not only to fail prematurely but also to corrode and swell so that removal of such a failed battery pack from its housing is often difficult if not impossible to do.